Remove the 'svnauth' tool, superseded by 'svn auth'.

* build.conf: Remove entry for 'svnauth'.

* subversion/svnauth/svnauth.1,
  subversion/svnauth/svnauth.c,
  subversion/svnauth: Remove.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1572110 13f79535-47bb-0310-9956-ffa450edef68